The invention relates to a device for steering the front wheel of a motor vehicle.
Italian Pat. No. 1 171 971, property of the same applicant, discloses a steering device of the type in question, which is designed to overcome certain drawbacks typical of the front suspension forks of motor cycles. The problems encountered with these front forks, which consist generally in a pair of telescopic damper struts located one on either side of the front wheel and carrying the relative pivot, derive from the difference in reaction of the two dampers and their inability to absorb shock from minor surface irregularities while compensating smoothly at the same time for major irregularities. The device in question was also designed to address new problems stemming from previous devices, which had succeeded in overcoming the drawbacks typical of front forks but required a non-symmetrical wheel and did not permit of designing an efficient and easily handled motor cycle.
The patent device referred to above consisted in a first hub carrying the front wheel, a second hub mounted coaxial with, internally of and rotatable in relation to the first, a steering pivot located internally of the second hub, perpendicular and rotatable with respect thereto about its own axis, and an axle pivot disposed at right angles to and rigidly associated with the steering pivot.
The axle pivot, disallowed rotation about its own axis, was permanently associated with the frame of the motor cycle by way of a parallelogram linkage. A lever associated with the second hub emerged from the first hub and was hinged by its projecting end to control means operated from the handlebars.
The inventor of the device envisaged the use of hydraulic control means, for example a fluid power cylinder installed between the lever of the second hub and the parallelogram linkage, which would be operated by the handlebars.
Whilst such a system might appear contemporary, given its similarity to servo linkages adopted in the great majority of motor vehicles to give easier handling, the drawbacks betrayed are nonetheless unacceptable for a machine intended for road use, and more especially for use in competition.
A first drawback is that of an insufficient level of safety, given that the cylinder can only operate if connected to a pressurized hydraulic circuit.
This can be achieved either by using the engine of the vehicle to pressurize a hydraulic circuit into which the cylinder is connected, or by connecting the cylinder into an independent hydraulic circuit pressurized by a gas accumulator.
In either case, there are drawbacks: in the first instance, the front wheel can be steered only when the engine of the motor vehicle is running, whereas the second option involves an additional and not infrequent routine servicing operation. In effect, the gas in a container of the type in question must be charged at high pressure (a significant number of atmospheres) in order to function effectively, but this same high pressure, besides increasing the likelihood of leaks, cannot be topped up utilizing normal low cost compressors. Accordingly, whilst a pressurized gas supply guarantees safe operation even with the engine off, the guarantee is limited in terms of duration, and if the acceptability of such a solution is doubtful enough in the case of a competition machine, it must be totally excluded in a standard production machine for obvious reasons. Yet another drawback connected with the hydraulic control is that of its own inertia; notwithstanding the high pressure to which the fluid operating the hydraulic cylinder is subject, movement of the handlebars is not transmitted instantaneously to the front wheel. Such inertia is hazardous in a road machine, especially when effecting sharp and sudden maneuvers, but altogether intolerable in a competition machine where swift handling response is a fundamental requirement.
Accordingly, the object of the present invention is to provide a steering device for motor vehicles, possessing the necessary precision and swiftness of response typical of a normal front fork, together with the positive features characteristic of the patent system outlined above.